Corynebacterium diphtheriae - Diphtheria


Indications for Testing

  • Presence of pseudomembrane; pharyngitis with other organ involvement

Laboratory Testing

Differential Diagnosis

Clinical Background

Classic diphtheria is characterized by pseudomembrane formation on respiratory mucous membranes.


  • Incidence – very rare in U.S. due to vaccination
  • Age – usually children <15 years who are unvaccinated or incompletely vaccinated  
  • Transmission – airborne or direct contact (respiratory secretions or skin lesion)


  • Non-spore forming, unencapsulated, pleomorphic, gram-positive bacillus
  • Produces exotoxin that causes many of the symptoms
  • Asymptomatic carriage occurs in some patients


  • Virulence is mediated by prophage-encoded exotoxin
  • Toxin induces dense necrotic coagulum on mucous membranes
    • Causes underlying soft-tissue edema

Clinical Presentation

  • Incubation period – 2-4 days
  • Respiratory tract
    • Anterior nasal disease
    • Faucial disease – classic membranes on pharynx and tonsils, cervical adenopathy and fever
    • Laryngeal and tracheobronchial disease – hoarseness, dyspnea, stridor, and brassy cough
  • Cardiac disease – myocarditis
    • Mortality 3-4 times that of patients without cardiac involvement
    • Related to toxin release
  • Neurologic disease – demyelinating neuropathy
    • Related to severity of disease – rare in mild disease
    • Usually motor neuropathy
  • Renal disease – proteinuria, renal failure
  • Cutaneous disease – chronic nonhealing ulcers with dirty gray membrane, often in mixed infections with Staphylococcus aureus and group A streptococci
  • Invasive disease


  • Vaccination


  • Diphtheria antitoxin
  • Antibiotics
  • Supportive therapy
  • Early ICU support for lower respiratory symptoms

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential

Identify infectious process

Streptococcus (Group A) Rapid with Reflex to Culture 0028903
Method: Immunoassay/Culture

Rule out more common cause of pharyngitis

If Streptococcus (Group A) Rapid test is negative, culture will be added for confirmation

Negative rapid test does not rule out presence of group A streptococcus

Corynebacterium diphtheriae Culture 0060360
Method: Culture/Identification

Identify organism causing pharyngitis

Occasionally patient may have asymptomatic carriage of diphtheria organism

Additional Tests Available
Click the plus sign to expand the table of additional tests.
Test Name and NumberComments
Diphtheria & Tetanus Antibodies, IgG 0050595
Method: Quantitative Multiplex Bead Assay

Confirm antibody production with pre- and postvaccination testing

Diphtheria Antibody, IgG 0050210
Method: Quantitative Multiplex Bead Assay

Determine patient's response to protein toxoid (majority of this antibody falls within IgG/subclass 1)

Diagnose antibody deficiency in patients with recurrent infections (especially sinopulmonary and gastrointestinal infections)

Diphtheria, Tetanus, and H. Influenzae b Antibodies, IgG 0050779
Method: Quantitative Multiplex Bead Assay

Determine if vaccine recipient responded to vaccine and if protective antibody levels have been reached

Determine IgG antibody titers to tetanus and diphtheria toxoids and H. influenzae PRP simultaneously